Wound healing is a complex process involving such factors as cells, extracellular matrix components and the cellular microenvironment. Essentially, all wound healing involves the repair or replacement of damaged tissues including but not limited to skin, muscle, neurologic tissue, bone, soft tissue, internal organs or vascular tissue. The precise nature of such repair or replacement depends upon the tissues involved, although all such processes involve certain basic principles. An important aspect of wound healing is the rate at which a wound gains tensile strength.
Skin exhibits tension and extensibility. Skin tension is one of the determining factors in the response to a wound and varies with age and site. Skin has multiple layers, including keratin, epidermis and dermis and contains cells, a fibrous network composed of collagen and elastin and an amorphous ground substance which consists of protein polysaccharides, glycoproteins, globular proteins, salts and water. If only the epidermis is damaged, as in most minor injuries, keratinocytes migrate from the edge of the wound and eventually cover it, reforming the epidermis and keratin (Knighton, D. R. and Fiegel, V. D., 1991, Invest. Radiol: 26:604-611).
If all skin layers are damaged or destroyed, new connective tissue, called granulation tissue, must first fill the wound space. This tissue is formed by deposition of extracellular matrix components, for example, collagen, by fibroblasts which migrate into the wound space. The synthesis and deposition of collagen is an important event in wound healing and the rate of collagen synthesis varies in different organs (Haukipuro, K. et al., 1991, Ann. Surg. 213:75-80).
The entire multi-step process of wound healing must be completed for successful would healing. If one or more of these components is missing, healing does not take place, the skin is not repaired and the wound remains open. Such open wounds can easily become infected, further retarding the process of healing and leading to the formation of ulcers and sores on the skin. The process of wound healing is further inhibited in many patients by the presence of other complicating conditions, including, but not limited to diabetes or old age. Patients with such conditions often have skin wounds which ulcerate and refuse to heal, or only heal slowly after an extended period of time has elapsed.
Various treatments have been used in order to accelerate the rate at which wounds heal (U.S. Pat. No. 4,772,591; U.S. Pat. No. 4,590,212) and various pharmaceutical carriers have been employed to deliver chemotherapeutic agents to the wound, for example, creams, gels, powders and microspheres. U.S. Pat. No. 5,264,207 discloses microspheres of a polymer, which act as carriers for one or more active pharmaceutical or cosmetic substances. The polymer microspheres are solid or hollow, insoluble in the carrier liquid and are of varying dimensions, not exceeding 1000 nm (1 .mu.m), with the preferred sizes ranging from 50 to 500 nm (0.05 .mu.m to 0.5 .mu.m) and the most preferred sizes ranging from 60 to 300 nm (0.06 .mu.m to 0.3 .mu.m). The fineness of the microspheres leads to higher specific area per unit weight and higher combination of microspheres to active substances without the disadvantage of conventional excipients which block skin pores. Thus, according to the invention of U.S. Pat. No. 5,264,207, a suspension of the microspheres can be obtained onto which an active substance is adsorbed, another substance binding to the microsphere by chemical bonds, with the possibility of a third substance binding to the microspheres by electrostatic or ionic bonds (Col. 2, lines 58-63). When the microspheres are hollow, they are both adsorbent and/or carriers of functional groups (Col. 3, lines 18-21). When the microspheres contain pores, bonding with a pharmaceutical or cosmetic substance consists of adsorption into the pores (Col. 3, lines 26-28). Thus, U.S. Pat. No. 5,264,207 discloses a composition of microspheres which act as carriers for pharmaceutical and/or cosmetic substances only and does not teach or suggest using only the microspheres themselves to enhance wound healing.
Similarly, PCT Application Nos. WO96/13164 and WO94/13333 both disclose microspheres made of a material which catalyzes the production or release of certain therapeutic substances. PCT Application No. WO96/13164 discloses polymeric nitric oxide adducts which release nitric oxide when directly applied to damaged tissue. PCT Application No. WO94/13333 discloses particles which are chemically modified to have free radical activity in the wound environment. Thus, neither reference teaches or suggests using the microspheres themselves as a therapeutic substance, without chemical modification of the microsphere material.
The size of the microspheres was shown to influence the effect of microspheres as carriers for the class I alloantigen used in the activation of cytotoxic T lymphocytes (Mescher, M. F., 1992, J. Immunol 149:2402-2405). The response was dependent on the class I antigen being presented on the optimum size of the microspheres of 4 or 5 .mu.m diameter (4000 nm or 5000 nm). In other words, Mescher disclosed that the activation of T lymphocytes in vitro could not be achieved with microspheres alone but required the class I antigen to induce the activation. The antigen reacted optimally when bound to microspheres of 4 or 5 .mu.m diameter, i.e. 4 to 5 times greater in size than microspheres used in U.S. Pat. No. 5,264,207, issued to Bommelser, J., et al. There is no teaching or suggestion in Mescher of using microspheres alone without the active component, class I antigen, in the activation of wound healing. In fact, the role of microspheres and cytotoxic T lymphocytes, in wound healing and collagen synthesis is not at all taught or suggested by Mescher. Furthermore, Bommelser teaches away from the use of microspheres greater than 1000 nm or 1 .mu.m in size because larger microspheres would block skin pores. Thus, the present invention is neither inherent (because of the difference in the ingredients of the compositions of prior art) nor obvious (because the size of microspheres used would be expected from prior art to block skin pores) from the prior art.
The process of wound healing includes an initial proliferative phase promoting rapid cell metabolism and proliferation, disposal of debris, mobilization of fibroblasts and restoration of circulation. It is during this period that the wound is most susceptible to infection. During the subsequent phase (also referred to as the fibroplastic phase) of wound healing, increasing tensile strength parallels the rise in collagen content of the wound. Thus, there has remained a need to develop compositions for wound healing such that they contain non-biodegradable microspheres and other extracellular components capable of promoting the proliferative phase and regulating the fibroplastic phase in situ.
Hence, there must be a balance between promotion of the proliferative phase and the onset of the fibroplastic phase during wound healing in animals and human beings for different conditions including, but not limited to, burned tissues, infections following surgery, surgery wound breakdown, internal ulcers, hemorrhage, bone gangrene, pressure sores, decubitis, compromised amputation sites, non-healing traumatic wounds, cosmetics, after shave, dental work, chronic ulcers (of the diabetics, varicose vein, post stroke), destruction of tissue by radiation, spinal injury wounds, gynecological wounds, chemical wounds, vessel disease wounds, diabetic skin sores, diabetic feet, physical trauma, post plastic surgery suture sites, sunburns or episiotomies.